In Brief

The inner lives of dolphins

Marine mammals carry an unexpected microbial mix

For more than 50 years, the U.S. Navy has used trained dolphins to find submerged sea mines and detect underwater intruders. Now it appears that the intelligent marine mammals have been hiding some secrets of their own. In a paper published Feb. 3 in Nature Communications, Stanford researchers say they discovered a startling variety of previously unknown bacteria living inside the dolphins, and to a lesser degree in U.S. Navy sea lions.

“About three-quarters of the bacterial species we found in the dolphins’ mouths are completely new to us,” says senior author David Relman, MD, professor of medicine and of microbiology and immunology. Lead author Elisabeth Bik, PhD, is a research associate in Relman’s lab.

What they’re learning about the microbial communities within marine mammals is not only a boon for zoology; it could prove useful for monitoring the health of the animals and their habitat, which is under siege from forces such as pollution, warming and overfishing.

Relman started working with the Navy dolphins more than 15 years ago, when he was asked to identify bacteria suspected of causing stomach ulcers in the animals. His efforts to catalog their bacterial communities were prompted by a request for a probiotic strain to keep the dolphins healthy. Navy trainers took regular swabs from the animals’ mouths and rectal areas, as well as obtaining gastric fluid from tubes the dolphins swallowed, samples of air the dolphins exhaled from their blowholes and sea water adjacent to each animal, and shipped them to Stanford for analysis.

Relman’s team also examined oral, gastric and rectal samples from the Navy’s trained sea lions, which revealed an interesting contrast: Even though the sea lions are fed the same fish as the dolphins, and swim in the same water, their bacterial communities are more like those of dogs and cats. The researchers’ next step is to look at samples taken from killer whales, sea otters, gray whales, harbor seals, elephant seals and manatees to understand the general impact of life in the sea on the marine mammal microbiota.

 “There’s a lot of concern about the changing conditions of the oceans and what the impact might be on the health of wild marine mammals,” Relman says. “Among other things, we would love to be able to develop a diagnostic test that would tell when the marine mammals are beginning to suffer from the ill effects of a change in their environment.”

Steve Fyffe is a communications manager for the Stanford Center for International Security & Cooperation.

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